Fixing crusty old chat addon, Lynchat for 9.0

[tordenflesk]

As you might see I've done the generic " add "BackdropTemplateMixin and "BackdropTemplate")" to createframe" that seems to fix a lot of my aging addons, but in this case it didn't change anything. Seemingly, the only function of the addon that doesn't work is stripping some edit-box highlighting
Error:

1x LynChat2\window.lua:257: attempt to call method 'SetBackdrop' (a nil value)
[string "@LynChat2\window.lua"]:257: in function <LynChat2\window.lua:190>
[string "@LynChat2\window.lua"]:302: in function `StyleTheChat'
[string "@LynChat2\window.lua"]:321: in main chunk

addon files attached.